U.S. patent number 7,666,508 [Application Number 11/805,159] was granted by the patent office on 2010-02-23 for glass article having a laser melted surface.
This patent grant is currently assigned to Corning Incorporated. Invention is credited to Jiangwei Feng, Stephan Lvovich Logunov, Robert Sabia.
United States Patent |
7,666,508 |
Feng , et al. |
February 23, 2010 |
Glass article having a laser melted surface
Abstract
A glass article having at least one edge of which at least a
portion has been laser melted. The laser melted portion scatters
light, thus enabling the glass article to be properly aligned. In
some embodiments, the laser melted portion also provides a
roughened edge having a coefficient of friction that facilitates
handling of the glass article. The laser melted portion is formed
by irradiating the peripheral surface with a laser beam to cause
localized melting.
Inventors: |
Feng; Jiangwei (Painted Post,
NY), Logunov; Stephan Lvovich (Corning, NY), Sabia;
Robert (Corning, NY) |
Assignee: |
Corning Incorporated (Corning,
NY)
|
Family
ID: |
40072679 |
Appl.
No.: |
11/805,159 |
Filed: |
May 22, 2007 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20080292845 A1 |
Nov 27, 2008 |
|
Current U.S.
Class: |
428/409; 65/61;
428/410 |
Current CPC
Class: |
C03C
23/0025 (20130101); Y10T 428/31 (20150115); Y10T
428/315 (20150115); C03C 2204/08 (20130101); Y10T
428/24421 (20150115); Y10T 428/24355 (20150115) |
Current International
Class: |
B32B
17/00 (20060101); C03C 19/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Blackwell; Gwendolyn
Attorney, Agent or Firm: Santandrea; Robert P.
Claims
The invention claimed is:
1. A glass article, the glass article having a peripheral surface,
the peripheral surface comprising a laser melted portion, wherein
the laser melted portion has a RMS roughness that is capable of
scattering light of a predetermined wavelength and a particle
release of less than about 650 particles/cm.sup.2 area of the
peripheral surface, and wherein each of the particles released is
greater than 2 .mu.m in size.
2. The glass article according to claim 1, wherein the peripheral
surface has a static coefficient of friction in a range from about
0.30 to about 0.60, as measured using a Teflon rod in dry
conditions.
3. The glass article according to claim 1, wherein the laser melted
portion is patterned.
4. The glass article according to claim 1, wherein the glass,
article is a fused silica article.
5. The glass article according to claim 4, wherein the fused silica
article is a liquid crystal display image mask.
6. The glass article according to claim 4, wherein the fused silica
article has an aspect ratio of at least 100.
7. The glass article according to claim 4, wherein the laser melted
portion is melted by irradiation with a CO.sub.2 laser.
8. The glass article according to claim 1, wherein the laser melted
portion has a RMS roughness of up to about 15,000 nm.
9. The glass article according to claim 8, wherein the RMS
roughness is in a range from about 100 nm up to about 15,000
nm.
10. The glass article according to claim 9, wherein the RMS
roughness in a range from about 100 nm to about 13,000 nm.
11. The glass article according to claim 1, wherein the
predetermined wavelength is in a range from about 500 nm to about
670 nm.
12. The glass article according to claim 1, wherein the light
scattered by the roughened peripheral surface, when measured at an
angle in a range from about 5.degree. to about 60.degree. to
incident light, has a normalized intensity I/I.sub.O in a range
from about 100 to 50 with absolute total scattering in a range from
about 1% up to about 20%.
13. A fused silica article, the fused silica glass article having a
roughened peripheral surface that is capable of scattering light of
a predetermined wavelength, wherein the roughened peripheral
surface comprises a laser melted portion, wherein the roughened
peripheral surface has a particle release of less than about 650
particles/cm.sup.2 area of the peripheral surface, wherein each of
the particles released is greater than 2 .mu.m in size.
14. The fused silica article according to claim 13, wherein the
peripheral surface has a static coefficient of friction in a range
from about 0.30 to about 0.60, as measured using a Teflon rod in
dry conditions.
15. The fused silica article according to claim 13, wherein the
laser melted portion is patterned.
16. The fused silica article according to claim 13, wherein the
fused silica article is a liquid crystal display image mask.
17. The fused silica article according to claim 13, wherein the
laser melted portion is melted by irradiation with a CO.sub.2
laser.
18. The fused silica article according to claim 13, wherein the
laser melted portion has a RMS roughness of up to about 15,000
nm.
19. The fused silica article according to claim 18, wherein the RMS
roughness is in a range from about 100 nm up to about 15,000
nm.
20. The fused silica article according to claim 18, wherein the RMS
roughness is in a range from about 100 nm to about 13,000 nm.
21. The fused silica article according to claim 13, wherein the
predetermined wavelength is in a range from about 500 nm to about
670 inn.
22. The fused silica article according to claim 13, wherein the
roughened surface scatters light that, when measured at an angle in
a range from about 5.degree. to about 60.degree. to incident light,
has a normalized intensity in a range from about 100 to 50 with
absolute total scattering in a range from about 1% up to about
20%.
23. A fused silica article, the fused silica article having a
roughened peripheral surface that is capable of scattering light of
a predetermined wavelength, wherein the roughened peripheral
surface comprises a laser melted portion, wherein the roughened
peripheral surface has a particle release of less than about 650
particles/cm.sup.2 area of the peripheral surface, wherein each of
the particles released is greater than 2 .mu.m in size, and wherein
the roughened peripheral surface has a static coefficient of
friction in a range from about 0.30 to about 0.60, as measured
using a Teflon rod in dry conditions.
24. The fused silica article according to claim 23, according to
claim 1, wherein the laser melted portion has a RMS roughness of up
to about 15,000 nm.
25. The fused silica article according to claim 24, wherein the
laser melted portion has a RMS roughness in a range from about 100
inn up to about 15,000 nm.
26. The fused silica article according to claim 24, wherein the
laser melted portion has a RMS roughness in a range from about 100
nm up to about 13,000 nm.
27. The fused silica article according to claim 23, wherein the
predetermined wavelength is in a range from about 500 nm to about
670 nm.
28. The fused silica article according to claim 23, wherein the
roughened peripheral surface scatters light that, when measured at
an angle in a range from about 5.degree. to about 60.degree. to
incident light has a normalized intensity in a range from about 100
to 50 with absolute total scattering in a range from about 1% up to
about 20%.
29. The fused silica article according to claim 23, wherein the
laser melted portion is patterned.
30. The fused silica article according to claim 23, wherein the
fused silica article is a liquid crystal display image mask.
31. The fused silica article according to claim 23, wherein the
laser melted portion is melted by irradiation with a CO.sub.2
laser.
32. A method of making a glass article having a roughened
peripheral surface, the method comprising the steps of: a.
providing a laser, the laser having a predetermined wavelength; b.
providing a glass article having a peripheral surface, wherein the
glass article absorbs radiation at the predetermined wavelength;
and c. melting at least a portion of the peripheral surface with
the laser to form the roughened peripheral surface, wherein the
roughened peripheral surface has a RMS roughness that is capable of
scattering light of a predetermined wavelength and a particle
release of less than about 650 particles/cm.sup.2 area of the
peripheral surface, wherein each of the particles released is
greater than 2 .mu.m in size.
33. The method according to claim 32, wherein the step of providing
a glass article having a peripheral surface comprises providing a
glass article having a peripheral surface that is ground, polished,
or etched.
34. The method according to claim 32, wherein the laser is a
CO.sub.2 laser.
35. The method according to claim 32, wherein the glass article is
a fused quartz article.
36. The method according to claim 32, wherein the roughened
peripheral surface scatters light of a predetermined
wavelength.
37. The method according to claim 36, wherein the predetermined
wavelength is in a range from about 500 nm to about 670 nm.
38. The method according to claim 36, wherein the roughened
peripheral surface scatters light that, when measured at an angle
in a range from about 5.degree. to about 60.degree. to incident
light, has a normalized intensity in a range from about 100 to 50
with absolute total scattering in a range from about 1% up to about
20%.
39. The method according to claim 32, wherein at least a portion
roughened peripheral surface has a RMS roughness of up to about
15,000 nm.
40. The method according to claim 32, wherein the glass article has
two major faces and wherein the method further including the step
of polishing the two major faces.
41. The method according to claim 32, wherein the step of
irradiating at least a portion of the peripheral surface with the
laser to form the roughened peripheral surface comprises rastering
the laser beam across the surface to create a pattern of localized
melting on the portion and resolidifying the pattern of localized
melting to form the roughened peripheral surface.
42. The method according to claim 32, wherein the glass article is
a liquid crystal display image mask.
43. A fused silica article, the fused silica glass article having a
roughened peripheral surface that is capable of scattering light of
a predetermined wavelength, wherein the roughened peripheral
surface is formed by: a. providing a laser, the laser having a
predetermined wavelength; b. providing the fused silica article
having a peripheral surface, wherein the fused silica article
absorbs radiation at the predetermined wavelength; and c. melting
the peripheral surface with the laser to form the roughened
peripheral surface, wherein the roughened peripheral surface has a
particle release of less than about 650 particles/cm.sup.2 area of
the peripheral surface, and wherein each of the particles released
is greater than 2 .mu.m in size.
Description
BACKGROUND OF INVENTION
The invention relates to glass articles having a roughened surface.
More particularly, the invention relates to glass articles having a
roughened peripheral surface or edge that is capable of scattering
incident light. Even more particularly, the invention relates to a
glass article having such an edge that has been roughened by laser
melting.
Glass articles, such as liquid crystal display image masks, require
relatively smooth, polished planar surfaces that are free of
physical defects or contamination. A rogue contaminant particle, if
pulled across the polished planar surface may, for example,
mechanically abrade the surface, producing a physical dig or
subsurface damage. Particle contamination may be generated by the
release of trapped debris (e.g., glass chips, lapping and/or
polishing compounds) originating from the ground edge of the glass
article during handling or from ultrasonic cleaning. The released
debris may work itself onto the polished surface of the article.
Another source of contamination is crack propagation originating
from subsurface damage. Such crack propagation releases glass chips
from the ground edge.
Glass articles such as image masks are often provided with ground
or otherwise roughened edges. Because of their light scattering
properties, such roughened edges assist in alignment of the glass
article. In addition, roughened edges facilitate manual handling of
the glass article. However, ground edges also act as a major source
of debris that may damage the polished surfaces of the article.
Thus, while providing a glass article with roughened edges is
highly desirable, it also is a major source of contamination.
Therefore, what is needed is a glass article having an edge that is
capable of scattering light and/or facilitating handling. What is
also needed is a glass article having an edge that has a low level
of release of debris. What is also needed is a method of making
such an edge.
SUMMARY OF INVENTION
The present invention meets these and other needs by providing a
glass article having at least one edge (also referred to
hereinafter as a "peripheral surface"), a portion of which is laser
melted. The laser melted portion scatters light, thus enabling the
glass article to be properly aligned. In some embodiments, the
laser melted portion also provides a roughened edge having a
coefficient of friction that facilitates handling of the glass
article. The laser melted portion is formed by irradiating the
peripheral surface glass article to cause localized melting.
Accordingly, one aspect of the invention is to provide a glass
article. The glass article has a surface comprising a laser melted
portion, wherein the laser melted portion has a RMS roughness that
is capable of scattering light of a predetermined wavelength and a
particle release of less than about 650 particles/cm.sup.2 area of
the surface, wherein each of the particles released is greater than
2 .mu.m in size.
A second aspect of the invention is to provide a fused silica
article. The fused silica glass article has a roughened peripheral
surface that is capable of scattering light of a predetermined
wavelength. The roughened peripheral surface comprises a laser
melted portion, wherein the roughened peripheral surface has a
particle release of less than about 650 particles/cm.sup.2 area of
the peripheral surface, wherein each of the particles released is
greater than 2 .mu.m in size.
A third aspect of the invention is to provide a fused silica
article. The fused silica article has a roughened peripheral
surface that is capable of scattering light of a predetermined
wavelength. The roughened peripheral surface comprises a laser
melted portion, wherein the roughened peripheral surface has a
particle release of less than about 650 particles/cm.sup.2 area of
the peripheral surface, wherein each of the particles released is
greater than 2 .mu.m in size, and wherein the roughened peripheral
surface has a static coefficient of friction in a range from about
0.30 to about 0.60, as measured using a Teflon rod in dry
conditions.
A fourth aspect of the invention is to provide a method of making a
glass article having a roughened peripheral surface. The method
comprises the steps of: providing a laser having a predetermined
wavelength; providing a glass article having a peripheral surface,
wherein the glass article absorbs radiation at the predetermined
wavelength; and irradiating at least a portion of the peripheral
surface with the laser to form the roughened peripheral
surface.
A fifth aspect of the invention is to provide a fused silica
article having a roughened peripheral surface that is capable of
scattering light of a predetermined wavelength, wherein the
roughened peripheral surface is formed by: providing a laser having
a predetermined wavelength; providing the fused silica article
having a peripheral surface, wherein the fused silica article
absorbs radiation at the predetermined wavelength; and irradiating
the peripheral surface with the laser to form the roughened
peripheral surface.
These and other aspects, advantages, and salient features of the
present invention will become apparent from the following detailed
description, the accompanying drawings, and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a planar glass article;
FIG. 2a is an optical image of a vertically oriented array of laser
melted areas on a peripheral surface of fused silica;
FIG. 2b is an optical image of a combined array of vertically and
horizontally oriented laser melted areas on a peripheral surface of
fused silica;
FIG. 3 is a plot of particle release from a fused silica article
before and after laser melting as a function of degree of surface
roughness;
FIG. 4 is a plot of normalized scattering intensity for 532 nm and
633 nm laser light as a function of scattering angle for fused
silica peripheral surfaces; and
FIG. 5 is a schematic representation of a side view of a glass
article having a peripheral surface comprising two chamfers.
DETAILED DESCRIPTION
In the following description, like reference characters designate
like or corresponding parts throughout the several views shown in
the figures. It is also understood that, unless otherwise
specified, terms such as "top," "bottom," "outward," "inward," and
the like are words of convenience and are not to be construed as
limiting terms. In addition, whenever a group is described as
either comprising at least one of a group of elements and
combinations thereof, it is understood that the group may comprise
any number of those elements recited, either individually or in
combination with each other. Similarly, whenever a group is
described as consisting of at least one of a group of elements and
combinations thereof, it is understood that the group may consist
of any number of those elements recited, either individually or in
combination with each other.
Referring to the drawings in general and to FIG. 1 in particular,
it will be understood that the illustrations are for the purpose of
describing a particular embodiment of the invention and are not
intended to limit the invention thereto.
A glass article having a surface comprising a laser melted portion
is provided. The laser melted portion has a RMS roughness that is
capable of scattering light of a predetermined wavelength. The
glass article also exhibits a particle release of less than about
650 particles/cm.sup.2 area of the surface. As used herein, the
term "particle release" means the total number of particles having
a size greater than 2 .mu.m released per unit area of the surface
(also referred to herein as the "edge" of the glass article) into
deionized water after agitation at 120 kHz with 370-400 W power for
4 minutes at room temperature. In some embodiments, the surface
from which particle release is measured is the peripheral surface
(also referred to herein as the "edge" of the glass article) of the
glass article.
Turning to FIG. 1, a planar glass article 110 is shown. The planar
glass article 110, which is representative of a LCD image mask
(also referred to herein as a "LCDIM"), has two major planar
surfaces 112 and four peripheral surfaces 114--also referred to as
herein as "edges." The terms "peripheral surface" and "edge" are
used interchangeably herein and are understood to be equivalent
terms. The glass article, however, need not be a LCDIM. The glass
article may also be, for example, a cylindrical glass article (not
shown), which may be an optical element, such as a lens, in a
lithographic stepper/scanner system. Such a cylinder has two faces
and a single peripheral surface. For the purposes of describing the
invention, planar glass article 110 will be described and referred
to unless otherwise stated.
In one embodiment, peripheral surfaces 114 comprise the laser
melted portion mentioned above. While the following description
describes the roughening of at least one peripheral edge, it is
understood that the roughened surface need not be a peripheral
surface of the glass article. Instead, it will be readily apparent
to one skilled in the art that other surfaces of the glass article
may be roughened by the techniques described herein.
Optical elements, such as lenses and LCDIMs, must be aligned
precisely within an apparatus, such as a lithographic
scanner/stepper system. Alignment is typically accomplished by
irradiating a roughened peripheral surface or edge 114 of the glass
article 110 with a laser beam 115 having a selected or
predetermined wavelength and using light scattered 117 from the
laser beam 115 back from or through peripheral surface 114 to align
the glass article 110. The predetermined wavelength is typically in
a range from about 500 nm to about 670 nm, with wavelengths of 532
nm and 633 nm being widely used. To facilitate detection of the
scattered light (and alignment of the optical element), it is
particularly advantageous to roughen at least a portion of
peripheral surfaces 114.
To date, roughening of peripheral surfaces 114 has been typically
achieved by grinding the peripheral surfaces 114. Such grinding
typically takes place during the forming of the glass article when
a near net shape is ground to meet the dimensional requirements of
the glass article. Grinding particles, glass chips, and other
contaminants released by the grinding process tend to migrate to
major planar faces 112 of the glass article 110, causing scratches
thereon. Debris generated by grinding also leads to crack
propagation during subsequent processing and handling of glass
article 110.
In the present invention, at least a portion of the peripheral
surfaces 114 is roughened by localized melting of the peripheral
surfaces 114. The localized melting is caused by irradiation of at
least a portion of peripheral surfaces 114 by a laser. The
localized melting of the peripheral surfaces 114 creates additional
roughness and opaqueness. The resulting RMS roughness is capable of
scattering light of the predetermined wavelength at a predetermined
scattering angle. In one embodiment, the predetermined wavelength
is in a range from about 500 nm to about 670 nm, with radiation
having a wavelength of either 532 nm or 633 nm commonly being used.
The scattered light has a normalized intensity ranging from about
100 to about 50, with absolute total scattering in a range from
about 1% up to about 20%, for scattering angles ranging from about
5.degree. to about 60.degree. to the incident light.
The laser is selected such that glass article 110 strongly absorbs
at the wavelength of the irradiating laser. Peripheral surfaces 114
of glass articles 110 formed from fused silica glass, for example,
are irradiated with a CO.sub.2 laser. However, any other suitable
laser such, for example, an excimer laser having a wavelength of
193 nm, may be used to irradiate the fused silica glass article
110. In one particular embodiment, the CO.sub.2 laser is a
continuous power rather than a pulsed laser. The laser may,
however, be pulsed at a frequency of at least 500 Hz, so as to be
quasi-continuous. The CO.sub.2 laser causes in situ localized
melting of the fused silica peripheral surface, but does not cause
subsurface damage that typically leads to debris generation.
Depending on the power regime used to irradiate the peripheral
surface, the localized melting of the fused silica peripheral
surface 114 creates either a depression or raised surface on the
irradiated area. Due to the low coefficient of thermal expansion
(CTE) of fused silica (5.5.times.10.sup.-7 cm/(cmK)), the residual
stress resulting from the laser melting procedure is minimal.
Glasses, such as soda-lime glass, having higher coefficients of
thermal expansion may be laser treated as well. In these instances,
the glass is preheated to at least 100.degree. C., laser treated,
and cooled slowly to minimize stress effects.
In one embodiment, the CO.sub.2 laser beam is rastered across the
peripheral surface 114, causing in situ localized melting of a
portion of the peripheral surface. Surface tension and localized
cooling effects combine to produce a warped surface which, upon
cooling, is rough and opaque. In one embodiment, this warped
surface has a RMS roughness of up to about 15,000 nm. In another
embodiment, the RMS roughness is in a range from about 100 nm to
about 15,000 nm. In yet another embodiment, the RMS roughness the
RMS roughness is in a range from about 100 nm up to about 13,000
nm. Rastering the CO.sub.2 laser beam across the peripheral surface
114 does not generate particles or subsurface damage that can
create particles during subsequent processing of handling.
Rastering the CO.sub.2 laser beam across the peripheral surface may
be used to form a laser melted portion of the peripheral surface
that is patterned. The pattern may be either periodic or aperiodic.
Alternatively, the laser melted regions may be disposed on the
peripheral surface in a random fashion. Non-limiting examples of
such patterns are shown in FIGS. 2a and 2b, which are optical
micrographs (100.times. magnification) of laser melted portions of
peripheral surfaces of fused silica. The patterns of laser melted
areas will affect the distribution of scattered light. Generally,
light is scattered in a direction perpendicular to a line of laser
melted material. For example, a pattern of vertically oriented
laser melted areas (FIG. 2a) provides light scattering primarily in
the horizontal direction. The pattern shown in FIG. 2b comprises
both horizontal and vertical lines of laser melted material, and
thus provides light scattering in both vertical and horizontal
directions.
The parameters of the pattern written by the laser may be varied by
changing the direction, period, and width of the laser melted
areas, as seen in FIGS. 2a and 2b. The dimensions of the laser
melted areas may be varied by altering beam diameter, power
density, and beam scanning speed.
In one embodiment, the CO.sub.2 laser operates in a continuous
power mode, with power varying from 2 to 30 W. The beam is focused
by a singlet lens with the focus spot at the peripheral surface--or
edge--of the LCDIM. The beam diameter may be changed by adjusting
the focus position. The minimum spot size of the beam may be 20
.mu.m. The LCDIM is translated by an X-Y stage at speeds of up to
100 mm/s. Alternatively, the LCDIM may be held in a fixed position
and the laser beam may be translated using either an X-Y stage or a
scanning mirror. Since the area to be roughened is not significant,
the entire procedure may take from 5 to 10 minutes. The treatment
time may be significantly reduced if only a portion of the
peripheral surface is to be roughened.
The release of particles from the peripheral surface when subjected
to a predetermined frequency of ultrasonic energy, also referred to
as "edge particle shedding," serves an indicator of the extent of
subsurface damage suffered by the peripheral surface during the
roughening process. Particle release is determined by agitating the
glass article at 120 kHz at a power of 370 W to 400 W in deionized
water for 4 minutes at room temperature. The release of particles
larger than 2 .mu.m from the peripheral surface of the glass
article is less than about 650 particles/cm.sup.2 area of the
peripheral surface. In one embodiment, release of particles larger
than 2 .mu.m from the peripheral surface of the glass article is
less than about 80 particles/cm.sup.2 under these conditions.
The effect of CO.sub.2 laser roughening on edge particle shedding
is shown in FIG. 3, which is a plot of the number of particles
released (expressed in particle count/10 ml deionized (DI) water)
in deionized water during sonic agitation under the conditions
previously described herein. To obtain the data shown in FIG. 3,
peripheral surfaces were first ground to grade 2 roughness (460 nm
RMS roughness) and grade 3 roughness (240 nm RMS roughness), as
determined by interferometry techniques known in the art such as
scanning white light or phase shift interferometry. Grades of
roughnesses are listed in Table 1. These peripheral surfaces were
then subjected to CO.sub.2 laser roughening. Edge particle
shedding--i.e., particle release--was measured before and after
CO.sub.2 laser roughening.
The results shown in FIG. 3 reveal that for all grades of
roughness, the peripheral surfaces that had been roughened by the
CO.sub.2 laser exhibit reduced levels of particle release. In
particular, the level of release from grade 1 and grade 2 surfaces
after CO.sub.2 laser roughening was at least an order of magnitude
less than those observed before laser roughening. Furthermore, the
particle counts observed for laser roughened peripheral surfaces
for all grades are less than 200 particles/10 ml deionized
water.
TABLE-US-00001 TABLE 1 RMS roughness Edge Grade Grinding Grit (nm)
0 600 581 1 Finer than grade 0 521 2 Finer than grade 1 459 2 Finer
than grade 2 236 4 Finer than grade 3 214 polished Much finer than
6.4 grade 4
The laser melted portion has a RMS roughness that is capable of
scattering light of a predetermined wavelength. The laser melted
portion presents a surface having a variable height that is
determined by spacing between laser scans and the spot size of the
laser beam. The laser melted portion may have a peak-to-valley
variation in height, which is reflected in its RMS roughness, while
having a smooth surface on a smaller scale. In one embodiment, the
laser melted portion has a RMS roughness of up to about 15,000 nm.
In another embodiment, the laser melted portion has a RMS roughness
in a range from about 100 nm up to about 15,000 nm. In yet another
embodiment, the RMS roughness is in a range from about 100 nm to
about 13,000 nm.
The effect of roughening by laser melting on scattering intensity
of different wavelengths of laser radiation is shown in FIG. 4.
Scattering intensities observed at angles of 30.degree.,
45.degree., and 60.degree. of laser radiation having wavelengths of
532 nm and 633 nm were measured for peripheral surfaces (curves a-j
in FIG. 4) of fused silica articles that had been ground to the
different grades of roughness listed in Table 1. Scattering
intensities for 532 nm laser radiation at the above three angles
were also measured for a polished peripheral surface before (curve
k) and after (curve l) melting by a CO.sub.2 laser. The scattering
intensity observed for the peripheral surface treated with the
CO.sub.2 laser is greater than those observed for all of the ground
surfaces and the polished surface.
In some instances, optical elements--particularly LCDIMs--are
handled manually. Accordingly, it should, in one embodiment, be
possible to frictionally grip the optical element on at least one
peripheral surface or a portion thereof. Thus, in one embodiment,
at least a portion the peripheral surface 114 has a static
coefficient of friction in a range from about 0.30 to about 0.60,
as measured using a Teflon.TM. rod in dry conditions. Thus, in one
embodiment, at least a portion the peripheral surface 114 has a
static coefficient of friction in a range from about 0.80 to about
0.50 as measured using a Teflon.TM. rod in dry conditions. The
static coefficient of friction is determined as follows. Friction
testing of edges (i.e., peripheral surfaces) is conducted in a
cylinder-on-flat geometry using Teflon rods (5.9 mm diameter). The
Teflon rods extend across the entire edge flat and beyond. A new
Teflon rod is used for each test. Testing is performed using a
commercial test machine that permits control and monitoring of
normal and lateral loads as well as the translation velocity. The
cylinders are loaded transversely onto the sample edge with the
desired normal load. This normal load is maintained constant
throughout the test. Sample translation is performed in a
reciprocating manner at a velocity of 0.5 mm/s over a distance of 5
to 10 mm. The static coefficient of friction and kinetic (dynamic)
coefficient of friction are determined using the guidelines
provided in pages 1-11 of ASTM G 115-04, entitled "Standard Guide
for Measuring and Reporting Friction Coefficients."
In one embodiment, the fused silica article is a LCDIM, in which
case it is particularly advantageous to provide roughened
peripheral surfaces or edges for articles having relatively large
dimensions. One measure of the dimension of such articles is the
"aspect ratio," which is the ratio of a diagonal of a planar
surface of the article to the thickness of the article. Aspect
ratios for planar articles of varying dimension are listed in Table
2. In one embodiment, a LCDIM having a laser melted peripheral
surface as described herein has an aspect ratio of at least
100.
TABLE-US-00002 TABLE 2 Diagonal Aspect ratio Length Width
(hypotenuse) Thickness (mm, thick vs. (mm) (mm) (mm) (mm) diagonal)
1220.0 1400.0 1857.0 13.0 142.8 800.0 920.0 1219.2 8.0 152.4 800.0
920.0 1219.2 10.0 121.9 800.0 960.0 1249.6 8.0 156.2 800.0 960.0
1249.6 10.0 125.0
In one embodiment, the peripheral surface further includes at least
one chamfer adjacent to and intersecting a major planar surface
(520 in FIG. 5) of the glass article. The chamfer is typically
formed during grinding of the near net shape. A profile of a
peripheral surface 514 having two chamfers 516 is schematically
shown in FIG. 5. In one embodiment, at least a portion of chamfer
516 is polished, producing a transparent chamfer. In another
embodiment, at least a portion of chamfer 516 has a RMS roughness
that is capable of scattering light of a predetermined wavelength.
The predetermined wavelength may be in a range from about 500 nm up
to about 670 nm. The predetermined wavelength may, in one
embodiment, be one of 532 nm and 633 nm. The RMS roughness may be
produced during grinding of the near net shape to within the
dimensional tolerances of the glass article by grinding chamfer
516. Chamfer 516 is relatively free of damage and generates an
interface with planar faces 520 that is free of checks and chips
greater than 5 .mu.m in size.
A method of making a glass article having a roughened peripheral
surface is also provided. A laser having a predetermined wavelength
and a glass article that absorbs radiation at the predetermined
wavelength are first provided. The glass article provided at this
step may be a near net shape of the final glass article. The
peripheral surface of the glass article may have been previously
ground, polished, or etched, or subjected to any combination of
these operations. For example, the peripheral surface may have been
previously ground while grinding a near net shape to within the
dimensional tolerances (i.e., to a dimension that is within a
predetermined tolerance of the prescribed dimensions of the glass
article) of the glass article.
Next, a portion of the peripheral surface of the glass article is
irradiated with the laser. The laser causes localized melting on
the surface, as previously described herein. The molten glass then
resolidifies to form the roughened peripheral surface. In one
embodiment, the step of irradiating a portion of peripheral surface
with the laser to form the roughened peripheral surface includes
rastering the laser beam across the peripheral surface to create a
pattern of localized melting on the portion and resolidifying the
pattern of localized melting to form the roughened peripheral
surface.
In those instances where the glass article has two major faces, the
method may further include polishing and cleaning the two major
faces.
Similarly, a method of roughening a surface of a glass article is
also provided. As previously described above, a laser having a
predetermined wavelength and a glass article that absorbs radiation
at the predetermined wavelength are provided. A surface of the
glass article is then irradiated with the laser, causing localized
melting of the glass on the surface. The molten glass then
resolidifies, forming the roughened surface.
While typical embodiments have been set forth for the purpose of
illustration, the foregoing description should not be deemed to be
a limitation on the scope of the invention. Accordingly, various
modifications, adaptations, and alternatives may occur to one
skilled in the art without departing from the spirit and scope of
the present invention.
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